BIOLOGY 153 - Cells, Metabolism, and Heredity

Spring 2001

The transmission electron microscope (TEM) is used to support lab
sessions for over 70 students in the Spring Intro Bio course. The TEM provides another way
to look at material that is also examined biochemically. In the lab exercise from the week
of Feb. 12, using both techniques made it possible to gather independent but mutually
supportive evidence that the enzyme succinate dehydrogenase is localized specifically to
the mitochondria.

Fig. 1 Electron micrograph (left) from the starting material, a
cauliflower mash prepared in lab. This mash will be further processed and then used to
study a subcellular component, the mitochondria, by spectroscopic means. The TEM image
shows the starting material, which predictably consists of large and small broken cell
fragments, clumps of dispersed DNA (chromatin), and free mitochondria.

Fig. 2 Electron micrograph (right) from the pellet that resulted
when the original mash was centrifuged at 600xG. Large cell fragments and clumped
chromatin are the major constituents of this preparation. There are few, if any,
mitochondria. (Approx. the same magnification as Fig. 1.)

Fig. 3 Electron micrograph (left) from the pellet that resulted when the
supernatant from the 600xG spin was centrifuged at 10,000xG. Very small cell
fragments and many mitochondria are present in this sample. When measured
spectroscopically, this sample demonstrated high levels of succinate dehydrogenase, an
enzyme that is specific to mitochondria. (Approx. the same magnification as Fig. 1.)

Fig. 4 A greatly magnified mitochondrion (below), which can be identified by its
double limiting membrane and the presence of internal membrane invaginations called
cristae. (Approx. 15X the magnification as Fig. 1.)